San Diego-based gene sequencing giant Illumina Inc. on April 2 rejected Roche Holding AG’s revised takeover bid, which values the company at about $6.7 billion.

Illumina President and CEO Jay Flatley said the board believes the new offer dramatically undervalues the company and “does not adequately reflect Illumina’s singular position in an industry poised for extraordinary growth.”

Roche on March 29 revised its original unsolicited offer to purchase Illumina, boosting its bid to $51 per share in cash from $44.50. Illumina’s board rejected that first offer on Feb. 8, calling it “grossly inadequate.” Since then, Roche has been trying to appeal directly to Illumina’s stockholders.

In response to Roche’s latest offer, Flatley again urged stockholders to hold on to their shares.

In a letter to Roche Chairman Franz Humer, Flatley said the Illumina board “remains of the opinion that Roche has made an opportunistic offer, fully aware that even the revised offer does not reflect the intrinsic strength or future prospects of Illumina.”

Illumina, looking ahead to its April 18 annual meeting, also is asking stockholders to vote in support of Illumina’s directors at the meeting. Swiss drugmaker Roche in January submitted a slate of four nominees for Illumina’s board of directors, and proposed five alternate nominees.

Roche is seeking to increase the size of Illumina’s board from nine to 11 directors, with the newly created directorships to be filled by candidates nominated by Roche.

In his letter to Humer, Flatley said the company believes its own strategic plan, “executed independently, will create stockholder value significantly greater than what you have proposed.”